1. Field of the Invention.
The present invention relates to the field of hot air welders used for welding thermoplastic material, and in particular, relates to hot air welders used for welding overlapping layers of thermoplastic roofing material.
2. Description of the Prior Art.
Conventional composition or asphalt roofs are now being replaced, particularly in commercial applications, by roofs covered and sealed by a thermoplastic sheet material. The thermoplastic material provides a superior, longer lasting roof which is ultimately more cost effective than composition or asphalt based roofs.
As with conventional roofing material, the thermoplastic roofing is manufactured in sheets and laid down on the roof in an overlapping manner in order to provide a weatherproof covering. Typically, one to three inches of material from adjacent sheets are overlapped and then welded together to form the weathertight seal. The heated overlapping thermoplastic sheeting is pressed together while in a soft, plastic state. The overlapping sections weld together as the soft plastic material from both overlapping portions intermingles and cools. A weathertight bond results. Any conventional means may be used to heat the overlapping layers to a plastic state including hand-held hot air blowers or large, flat soldering irons.
Since the number of running feet of such welds can be large, automated means have been devised to conveniently weld the overlapping sections of the thermoplastic sheets together. One such welder has been manufactured which is comprised of a three wheeled chassis having an electrically powered hot air blower mounted on the chassis, arranged and configured to deliver hot air to a shaped delivery port which is inserted between the overlapping sections of the thermoplastic sheeting. The welder is thus run down the length of the seam, thereby quickly and efficiently melting the adjacent surfaces of the thermoplastic material and then pressing the material together with a pressure wheel coupled to the chassis and positioned behind the shaped delivery port.
However, such a hot air welder is a relatively heavy and bulky device, measuring between one and two feet in width with a slightly greater length. The shaped delivery port through which the hot air is delivered is positioned on one side of the chassis and is held in a fixed orientation with respect to the chassis. The shaped delivery port must deliver air immediately to the adjacent surfaces of the overlapping thermoplastic material, and therefore must be shaped to reach around and between the overlapping sections of the sheeting. Depending upon which sheet is the top layer and the bottom layer of the overlapping section, the device must be positioned with respect to the overlapping section to allow the fixed, shaped delivery port to reach around and between the overlapping sections. In other words, if two sheets were laid with the left sheet overlapping the right sheet, the hot air welder would have to be positioned so that the delivery port could reach underneath the left and above the right sheet, extending generally from right to left. However, if the sheets were reversed so that the right sheet was above and overlapped the left sheet, the welder would have to be turned 180.degree. so that the shaped delivery port would reach underneath the right sheet and above the left sheet. However, as mentioned above, the fixed, shaped delivery port is set on one side of the chassis so that the width of the chassis must be accomodated by the roofing layout, if the welder is to be turned and used to weld both left and right seams.
Most roofs include a large number of vertical obstructions or parapets which are also covered with roofing material. The inflexibility of the prior art device requires that all seams be spaced from such vertical obstructions by one to two feet if the welder is to be used. As a practical matter, it is not always possible to arrange for the spacing of seams at a one to two foot distance from every vertical obstruction on a roof. Therefore, in many cases seams, which are too close and have an orientation such that the prior art welder cannot be used, are welded by hand using a soldering iron or hand-held hot air blower. The time required to make such seams by hand is large and represents one of the most expensive labor components in a typical roofing job. Furthermore, hand welding roofing seams is tedious work which requires careful attention if a perfect seam is to be made. Due to the tedium of the work, it is difficult to maintain the attention required to make a perfect seal.
What is needed then are improvements to a hot air welder which will allow the use of the welder to make both inside and outside seams so that the welder can be used to make seams which are in close proximity to vertical obstructions on a roof without the necessity for reversing the welder to accomodate a reversed seam.